1. Field of the Invention
The present invention relates to an air bag system including a horn switch mechanism which is provided on an upper side of a boss portion of a steering wheel of a vehicle which is situated near the center of the steering wheel.
2. Description of the Related Art
Conventionally, this type of air bag system includes a pad which is disposed on an upper side of a boss portion of a steering wheel, a mounting base on which the pad and a folded air bag are mounted and a plurality of switch members which make up a horn switch mechanism, which are mounted near an outer circumferential edge of the mounting base and which are configured to attach the mounting base to a steering wheel main body (refer to JP-A-2012-071716, for example). The pad includes a ceiling wall portion which covers the folded air bag from thereabove and which has a door portion configured to open by being pushed by the air bag which is being inflated and a side wall portion which extends into a cylindrical shape from a lower surface of the ceiling wall portion which lies around the circumference of the door portion so as to connect to the mounting base at a lower end thereof and which covers circumferentially a side of the folded air bag. Additionally, the air bag is fastened to be held to the mounting base around a circumferential edge of an inner circumferential surface of an inflation gas inlet opening of the air bag by an annular retainer which is attached to be fixed to the mounting base. Further, the switch members each include a movable-side member and an assembling pin as a fixed-side member. The movable-side member is disposed on an upper side, has a movable-side contact and is assembled to an assembling seat of the mounting base. The fixed-side member is disposed on a lower side, has a fixed-side contact which corresponds to the movable-side contact at an upper end side and is attached to the steering wheel main body at a lower-end side thereof which projects downwards from the mounting base. Furthermore, the switch members each include a coil spring which is disposed around the assembling pin as a biasing device for biasing a mounting base side upwards from a assembling pin side thereof. Additionally, a collar portion is provided at an upper end of the assembling pin so as to make up a controlling device for controlling a spacing distance between the movable-side contact and the fixed-side contact, and the collar portion is locked at a circumferential edge of an upper side of the assembling seat.
In the air bag system described above, however, the switch members are provided on the area outside the folded air bag on a mounting base, and further, the switch members are disposed so that the upper side of the movable-side member is brought into abutment with the lower end face of the side wall portion of the pad. Because of this, the assembling seat of the mounting base where the switch members are assembled is disposed further outwards than the air bag accommodating area. Additionally, the side wall portion of the pad is formed thick partially so as to be disposed further outwards than the air bag accommodating area to correspond to the movable-side members of the switch members which are assembled to the assembling seat. As a result of this, the air bag system itself is enlarged in size in such a way as to extend largely outwards from the circumference of the inflation gas inlet opening of the air bag.